To compare the response of human and rat red cells to DDS-NOH in regard to: a) methemoglobin formation; b) production of oxygen- and thiyl-radical (glutathiyl and hemoglobin-thiyl) species; c), sulfhydryl status; d),skeletal protein changes; e), echinocyte formatin; and f). macrophage ingestion. To determine the effect of inhibition of N-hydroxylation of dapsone on hemotoxicity in the acute and chronic rat models. To determine the relation between blood levels of DDS-NOH and hemotoxicity in volunteers and in patients receiving dapsone for the treatment of dermatitis herpetiformis and other disease. To examine the effect of the P-450 inhibitors:cimetidine, ketaconazole and grapefruit juice; and the commonly co-administered trimethoprim; on dapsone-induced methemoglobinemia and hemolytic activity.